israel has sealed off the main roads around gaza. will israel invade on the ground? >> i think the chances are going up. >> reporter: jeffrey white, a former analyst says an israeli ground invasion would be a brutal, bloody grind. >> a high density of population throughout the strip and highest in the major areas of gaza city, but there are a lot of civilians in other places, as well. but the other part of this is that hamas fights from inside the cities. >> reporter: cities of narrow streets, bazaars, apartment buildings. translation, a punishing building-to-building slog in a place that is slightly more than twice the size of washington, d.c. we used a google map with cnn contributor general james spider marks. what kind of combat are we talking about? >> combat in restricted terrain. in gaza city there are about 500,000 people that live in this city. you can only imagine the type of combat that is going to take place in this very restricted terrain. >> reporter: terrain where mark says israeli troops will be exposed to ambush, sniper fire, suicide bombings. if a g